Sterling cryocoolers are active-type cryocoolers employing inverse sterling circulation. Philips laboratory of Holland manufactured a pragmatic micro sterling circulation cryocooler for the first time in 1954, which could produce 580 W refrigeration capacity at 77 k. Such compactly structured Sterling cryocooler exhibited an attractive potential in industrial and military applications very soon. With improved technological levels and processing techniques, people use a highly efficient cool storing material, a precise clearance sealing technology, a flexible bearing design and advanced electronic technologies so that the Sterling cryocooler becomes very reliable, wearable and adapted for the cooling of low-temperature electronic devices, infrared detectors, superconductive devices and so on, and plays an important role in military and civil equipment such as missile guidance, infrared forward looking and night vision instruments and thermal imager.
Sterling cryocoolers in an early stage integrate a compression portion with an expansion refrigeration portion, and a compression piston and a displacer thereof convert a rotary movement of a motor into a simple harmonic movement of the piston via a crank linkage mechanism. A working medium flows alternately to and fro in the portions such as a compression space, a regenerator and an expansion space, without the mass of a gas changed, which forms a closed-type circulation. There are no valves in the machine for Sterling circulation so that an internal irreversible loss is small, so the machine exhibits a high efficiency, a compact structure, a small size and a light weight. However, the rotary movement of the machine causes a great vibration and a large noise. Except Philips cryocoolers for manufacturing liquid nitrogen and liquid hydrogen, Sterling cryocoolers have been developing in a tendency to miniaturization and longer service life to achieve highly efficient refrigeration in a liquid nitrogen temperature zone. These machines are mainly classified into integral type and separate type from structure so as to meet the requirements of many ground and spatial applications.
In tactical type Sterling cryocooler products in ground application, there are usually two types: a slip-on type and an integrated Dewar cryocooler assembly. Displacers of conventional cryocoolers are mostly disposed in a cylinder of a thin-walled stainless steel tube, a tiny clearance is provided between the displacer and the sleeve wall so as to ensure a contactless movement of the displacer and the cylinder wall, and presence of the sleeve cylinder allows the cryocooler to become an independent closed system. Hence, such structure is called a slip-on structure. A drawback of such slip-on structure is that when a cold finger of the cryocooler is cooled from 300 k to 77 k, a temperature gradient in a range of 300 K-77 K occurs on a sleeve of the displacer, and thermal conductance loss of the wall of the sleeve causes an effective refrigeration capacity of the cold finger to reduce. The integrated Dewar cryocooler assembly (IDCA) refers to a cryocooler assembly integrating a Dewar with a sensor. In view of the drawback of the slip-on structure with a sleeve, an inner cylinder of the Dewar is directly produced as a cylinder sleeve of the displacer, thereby omitting the outer sleeve of the conventional displacer, and obviating the thermal conductance loss of the sleeve wall to increase the effective refrigeration capacity of the sensor. Obviously, the integrated Dewar cryocooler assembly not only improves the thermal efficiency but also makes the system compactly-structured and reduced in size and weight, which is crucial to some applications.